The present invention relates to an automatic vehicle speed control device for use in automatic controlling the running speed of vehicle to a certain set speed.
As such an automatic vehicle speed control device, various constructions thereof are developed. For example, such an automatic vehicle speed control device comprises a vehicle speed sensor for outputting vehicle speed data proportional to an actual vehicle speed, a command switch for outputting cruise command signals, an actuator for driving a throttle valve, a vehicle speed memory means for memorizing the vehicle speed sensor data in accordance with operation of the command switch, a decision means for deciding whether or not the actual vehicle speed is within .+-. i km/h of the memorized vehicle speed during vehicle speed controlling, a setting means for setting a response constant G of the actuator at the time of transient response and for setting a response constant G-x of the actuator during a constant speed running by the decided result of the decision means, and a control means for controlling the actuator on the basis of a difference between the actual vehicle speed and the memorized vehicle speed with the response constant G or G-x of the actuator set by the setting means (See Japanese Patent Laid-open No. 205,828/87).
In the above, automatic vehicle speed control device, the command switch is subjected to its OFF operation after its ON operation, the vehicle speed at the OFF operation is memorized in the vehicle speed memory means (the vehicle speed at ON operation may also be memorized), a control signal is applied to the actuator by the control means in response to the difference between the actual vehicle speed and the memorized vehicle speed, and the throttle valve is driven by the action of the actuator in such a manner that the actual vehicle speed is made correspondent to the memorized vehicle speed, thereby effecting the constant speed running. When the actual vehicle speed exceeds in a range of .+-. i km/h the memorized vehicle speed during the constant speed running, the decision means decides this state, the setting means sets the response constant G of the actuator at the time of transient resoponse, and the control means supplies the control signal to the actuator, thereby adjusting the actual vehicle speed at the time of transient to the memorized vehicle speed quickly. Moreover, when the actual vehicle speed is within a range of .+-. i km/h of the memorized vehicle speed, this condition is decided by the decision means, the setting means sets the response constant G-x of the actuator at the time of constant speed running, the control means supplies a control signal to the actuator, thereby preventing the throttle valve from being adjusted than necessary, even when the actual vehicle speed is increased or decreased by external factor at the time of constant speed running.
In the above conventional automatic vehicle speed control device, some differences in performance of the actuator may arise due to the scattering in manufacture of the actuator, so that until now, the response constant G-x of the actuator at constant speed running has been set on the basis of lower limit of tolerance in manufacture. When the actuator is used by setting it at upper limit of tolerance in manufacture, and when the response time of the actuator is changed with temperature variation, however, the actual vehicle speed at the constant speed running becomes stable at higher speed than the memorized vehicle speed by about 1.about.2 km/h, and it often occurs that the actual vehicle speed does not correspond with the memorized vehicle speed, even with minimal adjustment of speed by deceleration control.